I'm trying to make the Bubbles Baby Blanket using the size N hook and two strands of worsted yarn. My work is too tight and the blanket is turning out too small and dense. I took it apart last night. I cannot seem to find the next size hook, which would be O. I have a P but it is much larger than the N.

Is there such a thing as a size O hook? I could not find one online. Would sizing down in the yarn help, maybe sport weight? I bought all this yarn in worsted.